let data = [
  {
    key:'1',
    pKey: '-1',
    title: '一级目录1',
    children: []
  },
  {
    key:'2',
    pKey: '-1',
    title: '一级目录2',
    allTitle: '一级目录1/一级目录2',
    children: [
      {
        key:'2-1',
        pKey: '2',
        title: '二级目录1',
        children: []
      },
      {
        key:'2-2',
        pKey: '2',
        title: '二级目录2',
        children: []
      }
    ]
  },
  {
    key:'3',
    pKey: '-1',
    title: '一级目录3',
    children: [
      {
        key:'3-1',
        pKey: '3',
        title: '二级目录3',
        children: [
          {
            key:'3-1-1',
            pKey: '3-1',
            title: '三级目录1',
            children: []
          },
          {
            key:'3-1-2',
            pKey: '3-1',
            title: '三级目录2',
            children: []
          }
        ]
      },
      {
        key:'3-2',
        pKey: '3',
        title: '二级目录4',
        children: []
      }
    ]
  }
]